Gap Junctional Coupling Underlies the Short-Latency Spike Synchrony of Retinal Ganglion Cells

We examined whether coupling between neighboring -type ganglion cells ( -GCs) in the rabbit retina underlies their synchronous spike activity. Simultaneous recordings were made from arrays of -GCs to determine the synchrony of both spontaneous and light-evoked spike activity. One cell within each array was then injected with the biotinylated tracer Neurobiotin to determine which of the cells were coupled via gap junctions. Cross-correlation analyses indicated that neighboring off-center -GCs maintain short-latency ( 2.5 msec) synchronous spiking, whereas the spontaneous spike activities of on-center -GC neighbors are not correlated. Without exception, those off-center -GCs showing synchronous spiking were found to be tracer coupled to both amacrine cells and neighboring off-center -GCs. In contrast, on-center -GCs were never tracer coupled. Furthermore, whereas spikes initiated in an off-center -GC with extrinsic current injection resulted in short-latency synchronized spiking in neighboring off-center -GCs, this was never seen between on-center -GCs. These results indicate that electrical coupling via gap junctions underlies the short-latency concerted spike activity of neighboring -GCs.